A slide idea was Re: gluing teflon and such - anodizing

Dave,

I missed most of this thread so I don't know what size the overall
machine is...

If the outer square tube has a wall of about 1/4 inch or so, you
could thread it, say 10-32 and use setscrews against a thicker uhmw
bearing plate (or metal pad with teflon face) on two of the sides.
The other 2 would have sheet uhmw/teflon as you already planned...
Hex nuts outside (on the setscrews) would lock the adjustment.

By allowing for adjustment, you eliminate the reliance on the exact
size of "typical industrial extrusion" tolerances. The allowable
tolerance for most aluminum extrusions is bigger than you think. And
this technique comes with not too high a price of extra work, IMO.
I'd do it this way and use tubes with a 1/4 or so difference; o.d. to
i.d. Be sure to place the pads/screws near the corners for maximum
stiffness of the assembly...

Adjust the size and location of the screws and stationary pads to
meet load vs. friction needs.

Hope this helps,

Ballendo

P.S. depending upon load needs, you may even get by with setscrews
only. By using a uhmw or teflon tipped s/s. Be careful of cold flow
of teflon! BTW, I'd not use moglice for this, as I think you'll have
more problems.

P.P.S. Even 1/8 wall alum can safely be tapped for 10-32; that's 4
threads, and many nuts have fewer... Use a roll tap(TRF) to make
these threads stronger. (A good idea anyway, as there are no chips
either, in addition to the stronger threads.)

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "turbulatordude"
<davemucha@j...> wrote:

> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "snuffman5994"

<parker@m...>

> wrote:
> > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "turbulatordude"
> > <davemucha@j...> wrote:
> >
> > > Of course the first question is surface prep. if teflon is a

non-

> > > stick, how do you get it to stick ?
> >
> > There is a process we use that is a plasma etch. This enables you
> to
> > bond teflon.
> >
> > > am thinking about hard anodizing the aluminum before assembly

and

> > > need to find out more about surface conditions. Like, does
> > anodizing
> > > raise the surface and make for a rougher surface ?
> > >
> >
> > Hard anodic coatings actually penetrate the aluminum 50%. So if

you

> > require a .002" thick hard anodize .001" will penetrate below the
> > surface and .001" will be above the surface. The problem you

could

> > have is on the corners. Make sure you radius the corners to avoid
> > plating build up.
>
> Ok, this may be on the fringe of off topic, but the ram Z axis will
> be a square aluminum tube, with a sheet of some sort of
> plastic/polimer/epoxy/stuff (PPES) and then another square tube
> inside. the inner tube will go up and down and the outter tube

will

> be fixed.
>
> I was hoping to use a pair of tube with 1/8 difference and insert a
> couple pieces of 1/16 of the PPES as the bearing surface. then,

since

> the inner would move, make the inner part hard anodized to decrease
> the potential of wear.
>
> This set-up would lend itself to Moglice as the PPES, but that

would

> require more attention to detail.
>
> It sound like anodizing will raise the surface, decreasing my 1/8
> some degree, then whatever adhesive us used, will also decrease the
> space even more.
>
> am I asking too much from stock products ?
> would I be better off with Moglice or similar ?
>
> Dave